Increased risk of traffic accidents in subjects with latent toxoplasmosis: a retrospective case-control study

Abstract

Background: The parasite Toxoplasma gondii infects 30-60% of humans worldwide. Latent toxoplasmosis, i.e., the life-long presence of Toxoplasma cysts in neural and muscular tissues, leads to prolongation of reaction times in infected subjects. It is not know, however, whether the changes observed in laboratory influence the performance of subjects in real-life situations.

Methods: The seroprevalence of latent toxoplasmosis in subjects involved in traffic accidents (N=146) and in the general population living in the same area (N=446) was compared by a Mantel-Haenszel test for age-stratified data. Correlation between relative risk of traffic accident and a level of anti-Toxoplasma antibody titre was evaluated with the Cochran-Armitage test for trend.

Results: A higher seroprevalence was found in the traffic accident set than in the general population (Chi2MH=21.45, p<0.0001). The value of the odds ratio (OR) suggests that subjects with latent toxoplasmosis had a 2.65 (C.I.95= 1.764.01) times higher risk of an accident than the toxoplasmosis-negative subjects. The OR significantly increased with level of anti-Toxoplasma antibody titre (p<0.0001), being low (OR=1.86, C.I.95=1.14-3.03) for the 99 subjects with low antibody titres (8 and 16), higher (OR=4.78, C.I.95=2.39-9.59) for the 37 subjects with moderate titres (32 and 64), and very high (OR=16.03, C.I.95=1.89-135.66) for the 6 subjects with titres higher than 64.

Conclusion: The subjects with latent toxoplasmosis have significantly increased risk of traffic accidents than the noninfected subjects. Relative risk of traffic accidents decreases with the duration of infection. These results suggest that 'asymptomatic' acquired toxoplasmosis might in fact represent a serious and highly underestimated public health as well as economic problem.

Figure 1

Seroprevalence of latent toxoplasmosis The figure shows difference in seroprevalence of latent toxoplasmosis (%) between the representative sample of general Prague residents (controls) and the sample of Prague residents involved in traffic accidents between 1997–2000 (victims). For numbers of subjects in particular categories, see Table 1.

Figure 2

Positive concordance of ORs, reflecting relative risk of traffic accident, with anti-Toxoplasma antibody titre The figure shows the exact estimation of the ORs with their 95% confidence intervals. The numbers indicate number of subjects with particular titre (NSPT) among 446 controls (numerator) and NSPT among 146 victims (denominator). Statistical significance of the two-tailed exact Cochran-Armitage test for trend with age-stratified data was p < 0.0001.